Shin = 300, ordinal 21, reduced 3, no final form. Spelled in full, שין = 300+10+50 = 360.
Meaning
Shin is 'tooth' and one of the three mothers, the letter of fire (esh) and the initial of Shaddai, the name written on the mezuzah's scroll and worn in the tefillin. Its 300 is the length of Noah's ark in cubits, and the shin of the tefillin is written with four heads instead of three — an anomaly the tradition reads as a letter with another letter inside it.